Leakage of gasoline or fuel oil from storage tanks is a common cause of underground pollution. A leak or spill of such pollutants may spread underground as a plume. Whether as a leak or as the result of prolonged conditions in an industrial complex, pollutants may travel to great depths; the pollution may extend into various underground formations, and it may enter the aquifer; and the pollution may penetrate under the foundations of buildings. Removal and exposure of contaminated soil for treatment is often impractical, so that in situ remediation becomes necessary.
In addition to gasoline and fuel oil, other examples of pollutants that are frequently found in soil and ground water include motor oil, polychlorinated biphenyl (PCB), chlorinated ethylene solvent, benzene, toluene, ethyl benzene and xylene. These four latter substances are referred to by the acronym BTEX. The BTEX measurement is used as a quantitative determination of the contamination.
In situ remediation of underground hydrocarbon contamination makes use of chemistry of Fenton, which dates back to 1898. Hydrogen peroxide is used to oxidize organic pollutants, breaking down complex organic compounds into successively smaller-chain compounts, ultimately becoming non-hazardous carbon dioxide and water. A metallic salt is introduced as a catalyst, for separating the hydrogen peroxide into HO radicals; it is those radicals which react with the organic compounds.
For in situ treatment of underground pollution, hydrogen peroxide is introduced into the subsoil via wells; its distribution from the wells commonly depends on natural permeability and capillarity of the underground strata. Such distribution is inherently slow, so that the treatment may take many weeks or months.
Compressed air is recommended in U.S. Pat. No. 5,525,008 (Wilson, issued Jun. 11, 1996) for injecting and promoting more rapid spread of hydrogen peroxide and catalysts into the treatment site.